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coming off throttle I hear a whirring sound on other side of firewall. It had never done tis before. Not sure if it is a BOV or the waste gate causing this. The turbonetics waste gate is near firewall and turbo is on underside of manifold. I believe this is a first generation Dinan. Turbo all works well and pulls hard. Doesn't seam to have any issues. Just the sound coming off throttle. Any info would be appreciated. I'm not too knowledgeable on turbo, bought E28 with the set up and have enjoyed it immensely. TIA

May need more details. Have a video of the sound?

I don't . While driving I can't hold anything down to it. When I leave throttle off it's a whirring sound. Throttle on silence except for the sound of turbo which operates beautifully.

Maybe take a look and see if something is obviously disconnected?

Is it only when you are off the throttle and slowing down?

yes. just for those few seconds after leaving off throttle . had never done this before

Disconnected intake or bypass valve recirc hose or just a noisy bypass valve.

okay I'll check that out thank you

My recirculating setup (early m102) whistles every time I let off under boost. My buddy calls it the "whoosh I'm a dick" sound.

Yeah. This isn't that sound. The sound is something not natural to a properly operating turbo. It occurred after car got hot. The turbo works just as it did before except for this sound that now comes after leaving off throttle just on other side of firewall behind glovebox . I'm going to be pulling engine soon and will inspect everything including turbo to see if I can locate cause. This engine is going into my Arktisblau restoration so I'll be doing the once over on it.